The Australian Services Union (ASU) is going to the Fair Work Commission to stop the ATO shifting staff who do not want to move 25km west from Sydney CBD to Parramatta.

In a bulletin to members, the union said the ATO had decided to move its "service delivery" functions out of the Australian Tax Office's Goulburn Street, Sydney, office so it could move into the central Sydney office staff from Hurstville.

A conference will be held at Fair Work on September 1 after the union lodged its concerns Wednesday.  

The union said the ATO's plan was to save significant funds by not renewing the lease on its Hurstville office. 

But the ASU said the Tax Office has not allowed the relocation of staff to Parramatta to be on a voluntary basis where practicable to the fullest extent as required by the bargaining agreement. 

"The ATO would not tell the ASU about any alternatives to relocation for employees it would make available where the relocation would cause hardship to employees," the union said to members in its bulletin. 

"The ATO ought to create a range of vacancies at the Sydney office for appropriate employees."

ATO spokesperson said that under the enterprise agreement, the Tax Office had the ability to move staff between sites within metropolitan areas.

"The Sydney CBD to Parramatta is considered to be within the same metropolitan area," the spokesperson said. 

"Staff and unions were advised of the final decision on May 15 after a two-week consultation period.

"Staff have had several months to consider this decision and discuss their circumstances with their manager.

"They have also been advised of their options if they feel they are unable to relocate. We will continue to work with our staff to make this transition as smooth as possible, consistent with our enterprise agreement."